Acoustical surfaces are used in those areas where sound absorbing qualities are necessary. A common area where such materials are found is in buildings wherein acoustic tile is commonly used to cover the ceiling. These tiles are often white or near-white in color. Acoustic tiles of this type are generally composed of porous layers of mineral or vegetable fibers bonded together with non-thermoplastic resins. The tiles may also be composed of glass fibers. The acoustic tiles of this type are provided with substantial porosity in order to absorb sound waves which emanate within the room. This porosity is evidenced on the surface of the acoustic tiles by the presence of small recesses or pores of varying diameter which permit the sound waves to enter the material and be dispersed.
Because the tiles are white, they become discolored as dirt and grease deposits accumulate on them. Further, becasue of the porosity of the fiber layers making up the tiles, they are difficult to clean. Detergents have been used to try and clean the tiles, but detergents may dissolve the dirt to the point where it becomes liquid and is trapped in the pores of the fiber layer. On cleaning by wiping, streaking may occur.
Since the porous tiles are so difficult to clean, a second option is to cover the tile surface with paint. Conventional paint has many disadvantages, however, primarily because the paint clogs the pores of the fiber layer, thereby reducing the sound buffering properties of the tile. Further, paint tends to make the tile hard and brittle, rendering it more susceptible to damage if struck. Therefore, because of the difficulties of cleaning the tile, and the disadvantages of painting it, the most common form of maintenance is simply replacement. However, this is obviously expensive.
The present invention provides a method utilizing a coating compsition which can be applied to acoustic surfaces with excellent results. Similar coating compositions are known in the prior art but are known for use in different areas. Thus, in U.S. Pat. No. 4,135,945, there is disclosed an aqueous pigment dispersion which contains a pigment component, such as titanium dioxide, a surfactant, water, and a biocide. U.S. Pat. Nos. 4,167,420 and 4,167,421 disclose paint dispersions which contain titanium dioxide pigment, together with quaternary ammonium dispersing agents. U.S. Pat. No. 3,929,705 discloses surface coating compositions which are aqueous solutions of water, biocides, surfactants, and titanium dioxide pigment.